In the past various devices have been employed with outboard and outboard-inboard motor boats providing socalled power trim units for the boat to vary the planing attitude of the boat and motor tilt devices to vary the tilt of the motor with respect to the boat transom. Such devices have included trim gauges of one type or another to indicate the degree of tilt of the outboard portion of the motor with respect to the transom. Such indicators may also indicate the distance that the motor is moved away from the transom which is simply another form of tilt indication with respect to the transom.
Such devices do not indicate the relative position of the outboard motor with respect to the water and give no accurate indication of whether the axis of the propeller is parallel to the line of travel of the boat or in other words whether it is parallel to the surface of the water. In such parallel condition the motor should be perpendicular to the surface of the water or line of travel of the boat.
It has long been a problem to present the maximum propulsion force in such boats both for economy purposes and high speed performances. Such problems are well typified by an upward direction of thrust of the propeller causing the well-known "rooster-tail" with a consequent loss of energy and fuel and a downward thrust causing a bow-heavy boat.